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- Volume 21, Issue 3, 2023
Near Surface Geophysics - Volume 21, Issue 3, 2023
Volume 21, Issue 3, 2023
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Finetuning ground penetrating radar velocity analysis from hyperbola fitting using migration
More LessAbstractThe widely used tool, ground penetrating radar (GPR), has proven to be an excellent research method for glaciological studies. The total ice thickness and englacial structures can be studied, and the method can give information on the temperature regime within the ice. Good velocity profiles are needed to convert measured two‐way travel time to depth information. In addition, a good velocity analysis can be used to improve data processing. A number of methods can be used to find the GPR wave velocity, which are briefly described. This study used hyperbola fitting to estimate the velocity in a glaciological study. In addition, Kirchhoff's migration was used to fine‐tune this velocity estimate. Within the Longyearbreen glacier, situated next to Longyearbyen on Spitsbergen, Svalbard archipelago, objects in the ice act as scattering points that create hyperbolas. Using the hyperbola‐fitting method, a GPR wave velocity equal to 0.170 ± 0.005 m/ns was estimated. By doing Kirchhoff's migration and studying the collapse of hyperbolas with variations of the migration velocity, a more accurate velocity estimate can be achieved; 0.172 ± 0.002 m/ns. A more accurate velocity estimate like this opens possibilities for better characterization of the ice body and ice thickness variations, as well as the variation of these as a function of time. In March 2022, the maximum ice thickness in the investigated area was calculated to be 88 ± 1 m.
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An improved correlation stack method for near‐surface seismic data
Authors Xinglin Lu, Wei Wang, Xuquan Hu, Xian Liao, Zhixiong Fu, Chaopeng Luo, Zheng Xu and Zhihong FuAbstractThe seismic reflection method is the primary tool to provide detailed information on the near‐surface. This paper proposes a common receiver correlation stack method. A towed seismograph is used to perform the rapid acquisition with small geophone spacing and a high sample rate, while broadband (from 1 Hz to 1000 Hz) seismic data are collected. Results of modelled and measured data indicate that the proposed stack method: (1) does not need normal move‐out velocity; (2) does not lose shallow information; and (3) improves the stacking fold by twice as much as the conventional stack method. Compared with the conventional stack method, the proposed method can suppress surface waves better and improve the quality of the final sack section, especially for high‐frequency data. Combined with the towed seismograph, the proposed stack method can perform the rapid collection and enhance the accuracy of stack imaging of near‐surface seismic data.
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Influence of input motion and surface layer properties on seismic site response: A stochastic simulation method–based MLR model
By Özgür YıldızAbstractSeismic site response analyses are simulations in which the effects of geological conditions on seismic waves are examined. The uncertainties that make these analyses crucial are defined as the source of motion, the travel path of seismic waves, and geological conditions. In this study, a series of non‐linear seismic response analyses were performed using data from site investigation studies. The results of non‐linear analyses performed under earthquakes with different characteristics based on real soil data were investigated in terms of acceleration time histories and response spectra. The relationship between site response with the surface layer properties and input motion properties used in the simulations was examined in a parametrical manner. Based on the results obtained, Monte Carlo simulation, which is a stochastic data simulation method, was performed. Additionally, multiple regression and variance analysis (ANOVA) was performed on the dataset created by both site response analysis and stochastic simulations. The MLR model displayed highly accurate results with a coefficient of determination, R2 of 0.9763, and a standard error of 0.109. The efficiency level of the independent variables used as input parameters in the simulations on the dependent variable, AF was examined. It was revealed that the coefficient of lateral earth pressure at rest (Ko), earthquake motion (i.e., PGA of input motion) and surface layer thickness (dsurface) from the soil properties had the highest effect on the amplification factor.
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Interpretation and modeling of aeromagnetic data from helicopter surveys of the Morobe goldfield, Papua New Guinea
Authors Mitchell S. Craig and Shadrach NokuAbstractWe interpreted and modelled aeromagnetic data from helicopter surveys of the Morobe goldfield, Papua New Guinea, by comparing gridded magnetic data with mapped surface geology. In some cases, geologic units may be recognized and distinguished based on contrasts in magnetic intensity and texture, including the Morobe Granodiorite, Kaindi Metamorphics, Bulolo Volcanics, and Langimar Beds. Magnetic anomalies occur due to intrusions of Edie Porphyry and related igneous rocks that are associated with gold mineralization. Numerous faults control the size and shape of the intrusions. Magnetic anomalies of interest were identified in gridded data from high‐resolution surveys and modelled using flight line data. Two‐dimensional magnetic models included dipping slabs with thicknesses of 100–400 m. Three‐dimensional models were prepared, including a dipping tabular body and a dipping cylinder. A 2008 survey of the Papuan peninsula sponsored by the European Union (EU) provided continuous coverage of the Morobe goldfield area and helped resolve regional features that were only partially covered by previous smaller surveys. In particular, the EU survey covers the full length of the Sunshine Fault and greatly extends coverage of outcrops of the Morobe Granodiorite and Langimar Beds. The EU survey contains isolated anomalies south‐west of Wau that may correspond to intrusions of Edie Porphyry, Morobe Granodiorite.
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3D joint interpretation of potential field, geology, and well data to evaluate a salt dome in the Qarah‐Aghaje area, Zanjan, NW Iran
Authors Hosseinali Ghari, Ramin Varfinezhad and Saeed ParnowAbstractAs geophysical parameters are not always functionally related, treating multiple geophysical data sets to have a realistic geological model is not straightforward. An effective strategy to derive a geological interpretation is a combination of several geophysical methods with geological and well observations, each with its advantages and limitations. Gravity and magnetic methods are encouraging tools to investigate salt domes due to enough density and susceptibility contrasts between salt minerals and the background sedimentary rocks. In this paper, the dome‐shaped salt unit in the Qarah‐Aghaje area in Zanjan, located in the northwestern part of Iran, is investigated through the integration of 3D inversion models obtained from gravity and magnetic data and geological and well information. The 3D inversion of both data sets is made using a weighted damped minimum length solution for which model weighting is constructed from multiplying depth weighting and compactness constraints. At first, a synthetic case with a high degree of similarity to the real case is considered to evaluate the efficiency of the adopted inverse algorithm. Then, the inversion algorithm is implemented on the collected gravity and magnetic methods, and interpretation is made utilizing 3D obtained inverse models and geologic and well data. The result shows a dome‐shaped potash‐bearing salt unit that starts from a depth of 12 m and continues to the depth of 200 m. The drilled well in the centre of the main source of the salt (Well 3) demonstrates a depth range of 11–115 m.
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Volumes & issues
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Volume 22 (2024)
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Volume 21 (2023)
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Volume 20 (2022)
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Volume 19 (2021)
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Volume 18 (2020)
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Volume 17 (2019)
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Volume 16 (2018)
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Volume 15 (2017)
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Volume 14 (2015 - 2016)
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Volume 13 (2015)
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Volume 12 (2013 - 2014)
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Volume 11 (2013)
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Volume 10 (2012)
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Volume 9 (2011)
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Volume 8 (2010)
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Volume 7 (2009)
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Volume 6 (2008)
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Volume 5 (2007)
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Volume 4 (2006)
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Volume 3 (2005)
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Volume 2 (2004)
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Volume 1 (2003)